The invention relates to a friction feed wheel mechanism with vibration excitation.
So-called friction feed wheel mechanisms are often employed for feeding thread to thread-processing machines, in particular those, which have a chronologically fluctuating or intermittent thread requirement. These have a thread feed wheel, which is driven at a constant number of revolutions and has a contact surface for the thread. The thread is wrapped around the thread feed wheel at a wrap angle which is mostly less than 360xc2x0. The thread is moreover conducted through the eye of a thread guide lever, wherein the position of the lever affects the wrap angle. The thread guide lever is usually pre-stressed away from the thread feed wheel by means of a spring force. When the use of thread by the thread-processing machine ends, the thread guide lever slightly lifts the thread off the thread feed wheel or reduces the wrap angle, so that the thread feeding is stopped. Thus, the thread usage controls the thread feeding.
The coefficient of friction which prevails between the thread and the contact surface is important for the functioning of such a friction feed wheel mechanism. In actual use, the coefficient of friction changes because of matter being carried along by the thread, such as oil, wax or other materials and being deposited on the contact surface. Because of this, as well as because of the aging of a possible friction lining, for example a plastic material or rubber, the feeding properties of the device slowly change. If the coefficient of friction between the friction lining and the thread is large, the thread tends to adhere to the friction lining. The result of this can be that the friction-controlled switch-off, i.e. the stoppage of feeding by the friction feed wheel mechanism, does not take place correctly. For example, the thread is not detached from the drum when the thread guide lever is pivoted out and its feeding is therefore continued. Even if the thread is detached from the friction lining, damage of the thread and/or of the friction lining can occur because of the remaining contact between the thread and the thread lining of the rotating drum during extended periods of stoppage of the thread. Rubber linings are particularly endangered. Too low a coefficient of friction, however, can interfere with the reaction properties of the friction feed wheel mechanism, if a thread feed suddenly occurs and thread must again be fed in following a feeding stop.
A friction feed wheel mechanism is known from U.S. Pat. No. 4,058,245 which, in view of the above mentioned problems, is provided with a special thread feed wheel. The thread feed wheel has a contact surface which is designed, for example, as a meander-shaped annular groove. In another embodiment, the contact surface is constituted by spokes of a wheel or by pins attached to a wheel, which are arranged crosswise, viewed in the circumferential direction, and are inclined at an acute angle in respect to the radial direction. A thread placed around the wheel lies in a zig-zag shape between the pins or spokes.
The division of the contact surface into individual surfaces and the zig-zag-shaped thread placement lead to conditions which differ from those occurring in connection with thread feed wheels which are coated with a plastic material or rubber and are essentially cylinder-shaped. Such friction feed wheel mechanisms are also dependent on the friction between the contact surface and the thread in regard to their reaction properties. The friction, in turn, is a function of the yarn type and the thread type.
Based upon the foregoing, it is the object of the invention to produce an improved friction feed wheel mechanism.
The friction feed wheel mechanism in accordance with the invention has a vibration generating device, which acts on the thread. This is accomplished, for example, in that it is connected with the thread guide lever, the thread feed wheel, a thread guide element or any other element touching the thread.
In this way the detachment of the thread from the contact surface of the thread feed wheel is made considerably more easy, in particular in case of a feed stop, and the remaining contact between the thread and the thread feed wheel is minimized.
If the thread adheres to the contact surface, it is possible to overcome the static friction by means of the vibration applied to the thread, the thread guide element, the thread feed wheel or the thread guide lever or other element, which considerably improves the removal properties (switching the thread feed off). This applies in particular, but not exclusively, to thread feed wheels having a coating with a large coefficient of friction or a structured surface, which permits good thread feeding. Moreover, this applies in particular to threads having a large coefficient of friction. A further advantage lies in that deposited dirt, which possibly can lead to adherence, such as sizing, oil or the like, does not lead, or leads less, to adherence of the thread. The step of exposing the contact between the thread and the thread feed wheel to a certain vibration, therefore drastically improves the thread removal, i.e. the disruption of the thread feed wheel which takes the thread along.
Because of the application of vibration to the thread it is possible for the latter to be lifted off the thread feed wheel almost completely when the thread is standing still, wherein at most a small area of contact between the thread and the thread feed wheel remains, in which the thread then rests against the thread feed wheel without or under only little tension. Because of this, long thread idle times are possible without damage to the thread or to the thread feed wheel.
The feed wheel mechanism in accordance with the invention can be employed for various threads with differing frictional properties. Because of the vibrational reinforcement, the correct functioning is not sensitive to changes in the coefficient of friction.
In the embodiment of the invention, the thread guide lever can be designed as a pivot lever, as well as a resilient hoop, or as any other shape. It is essential that it supports a thread guide element, whose position in respect to the thread feed wheel can be affected by the thread tension. In a simple manner, rigid levers permit the setting of a force which pre-stresses the lever, for example by means of a tension spring, whose point of suspension is adjustable. The setting of the force permits the matching to different thread tensions and thread qualities. Resiliently designed levers, however, lead to particularly simple structures. In both embodiments, the respective lever is attached to a seating device (xe2x80x9csecond seating devicexe2x80x9d) at its end remote from the thread guide element. If the lever is rigid, the second seating device allows a movable, for example pivotable, seating. Independently thereof, the seating arrangement (pivot bearing or a rigid version) can be connected with the vibration generating device, which causes the thread guide lever, and therefore also the thread guide element supported by the thread guide lever, to vibrate. These vibrations can be transferred to a larger or lesser degree to the thread via the thread guide element.
Alternatively or additionally, the first seating device for the thread feed wheel and/or a thread guide element, which is arranged upstream or downstream of the thread feed wheel, can be connected with the vibration generating device. A vibrational movement is respectively caused, which can be transmitted to the thread. In this connection the vibrating movement can be directed as needed. Possible are, for example, oscillations transversely in respect to the respective axis of rotation, linearly in respect to the respective axis of rotation or pivot axis, or obliquely in respect to it. If the vibration generating device acts on the thread guide element, which is arranged upstream or downstream of the thread feed wheel, the direction of vibration can be directed transversely in respect to the thread and parallel with the axis of rotation of the thread feed wheel, or transversely to the latter. The vibration generator can basically also perform a superimposed oscillation, so that the respective vibrating element is not only guided (swings) on a linear, but also an elliptical or circular path. In this case the vibrating movement becomes an orbital movement with a small radius.
It is considered to be particularly practical to design the contact surface of the thread feed wheel in an interrupted fashion. The contact surface can be defined by several strips, spokes, teeth or pins, which determine a zig-zag-shaped thread course, for example. This embodiment not only has good reaction properties, but also good removal properties. This applies to a great extent independently of the type of the thread used.
A particularly operator-friendly structure results if both the inlet thread guide element, placed upstream of the thread feed wheel, and the outlet thread guide element, placed downstream of the thread feed wheel, are arranged to be accessible from the direction of the operating side of the thread feed device, and if both the thread guide element of the thread guide lever and the thread travel path on the thread feed wheel are fixed on a section of the circumference of the thread feed wheel which faces the operating side. Therefore the thread need not be conducted behind the thread feed device in the course of being threaded, which makes the operation considerably easier.